
ICOM IC-720A ROTARY SWITCH REPLACEMENT MOD using RELAYS

Original pages, with latest news, pictures and informations:

http://zaverio.net/~asbesto/ic720amod
http://qrz.com/db/iw9hgs


   Hi, I'm IW9HGS, Gabriele "Asbesto" Zaverio, and this is my ICOM
   IC-720A Rotary Switch Mod!

   I made this mod starting from the F5IKI Rotary Switch Mod.
   I decided to simplify the mod itself, wiping out the PNP section 
   and the binary count logic, and using just a simple 4017 CMOS 
   counter instead of TTL logic. It works very well! 

   A brief description: the counting pulse from J1-7 is "filtered" using
   74HC00 NAND doors; it goes directly into the 4017, that start
   counting. The 4017 output goes to the 2222 transistor that drive the
   relay, and also goes to the diode matrix, to form the L1,L2,L4,L8
   binary code needed for the 720's microprocessor. The 4017 is powered
   directly to 7.5V, so there's no need to convert this level to obtain
   the binary code so the microprocessors can use it directly (in fact,
   the 720 uP need about 7V logic levels. I don't know why)
   I used the F5IKI boards he sent to me, so I haven't developed the PCB
   boards for this mod. Can someone build them, so I can add to this mod?
   Anyway, as a starting point, you will find the F5IKI pcb in the
   "Various mods" section.

   Many thanks to: F5IKI, that sent me the logic boards to do this mod
   and some components; IZ2LSL for helping and supporting me and for the
   1N4004 MELF diodes; WB0GAZ, ON4AZD and udomahr@t-online.de for
   documentation I found on the Internet, IRC Channel #retrocomputing on
   Azzurra.net for support and happiness, the Ari Fidenza Forum for
   support and help, and Acme (olocolors.org) for the LIFETIME TOOLS that
   really helped me a lot! ;)
   If you miss in the credits, or you think you have to be added, please
   write me and I will add you ASAP! ;)

   Feel free to contact me at the address iw9hgs(at)gmail(dot)com, or via
   QRZ.COM! ;)
   73 de IW9HGS - http://freaknet.org/asbesto

